Although the prior art discloses hydrocarbon tagging materials having molecular weights of up to 1,200, that art teaches away from using much higher molecular weight materials as tagging materials.
U.S. Pat. No. 4,141,692 teaches using chlorinated compounds as markers. These dyes have a molecular weight of less than 250.
U.S. Pat. No. 4,209,302 teaches using invisible colored dyes. These dyes have a molecular weight of less than 800.
U.S. Pat. No. 4,278,444 teaches using fluorescent dyes as markers. These dyes have a molecular weight of less than 800.
U.S. Pat. No. 4,735,631 teaches substituted anthraquinone tagging compound, which would have a molecular weight of less than 700.
U.S. Pat. No. 4,764,474 teaches using a substituted anthraquinone tagging compound, which would have a molecular weight of less than 700.
U.S. Pat. No. 4,918,020 teaches a method for analyzing marker dyes by using a solid-phase extraction technique with formation of a colored complex in the extraction column.
U.S. Pat. No. 5,234,475 teaches using one or more fullerene additives as tracers in a fuel. It teaches using up to C.sub.84 fullerenes, which would have a molecular weight of less than 1100.
European Application 0 509 818 A1 teaches silent markers as tracers in petroleum, such as 2,6-bis(1,1-dimethylethyl)-4- (4-nitrophenyl)azo-phenol!. The disclosed markers all have molecular weights of less than 900.